An outbreak of the terrifying
Ebola virus emerged in the West African nation of Guinea in
February and has been spreading ever since, infecting people in
Sierra Leonne and Liberia as well. The World Health Organization
announced new numbers on Tuesday, in what is now the biggest and
deadliest outbreak of Ebola since the virus was identified in
1976.

The disease's spread seemed to
slow down for a while, but has picked up in recent weeks.
Anestimated759
people have been infected, and 467 have died in Guinea, Sierra
Leone and Liberia. While it's likely that many cases go
uncounted, the Associated Pressnotesthat
previously, the largest reported death toll was in the Congo in
1976, when 280 people died. (Themost widespread outbreakinfected 425 people in Uganda in 2000,
killing 224.)

Recent investigations by public health
authorities suggest that the virus actually may have first
emerged undetected as early as December.

"The epidemic is now in a second wave," Bart Janssens, the
director of operations for Doctors Without Borders told the Associated Press. "It is
totally out of control."

"There needs to be a real
political commitment that this is a very big emergency," Janssens
added. "Otherwise, it will continue to spread, and for sure it
will spread to more countries."

This outbreak is unique because it has struck areas like Monrovia, the capital of Liberia, and Conakry, the
capital city of Guinea. Ebola usually emerges in sparsely
populated rural regions, where fewer people pass through.

The WHO identified three major factors that are
contributing to the continuing spread of Ebola:

"Strong cultural practices and traditional beliefs" in
rural areas mean that traditional funeral practices, fear, and
misinformation make the outbreak difficult to contain.

The disease, historically a product of primarily rural
areas, is now in densely populated cities.

Ebola has spread across the porous borders of Guinea,
Liberia, and Sierra Leone, where, the WHO notes, "commercial
and social activities continue."

"Major challenges faced by all partners in the efforts to control
the outbreak include its wide geographic spread, weak health-care
infrastructures, and community mistrust and resistance," the CDC
noted in a recent update.

In an interview with NBC News, Robert Garry, a
microbiology professor at the Tulane University School of
Medicine, warned that the outbreak so far is just "the
tip of the iceberg."

Still, in its latest update, the World Health Organization said it
"does not recommend any travel or trade restrictions be applied
to Guinea, Liberia, or Sierra Leone based on the current
information available."

Ebola is one of the deadliest viruses ever known, with the most
fatal strains killing up to 90% of people infected. The current strain has killed closer to 60% of
those infected, based on the numbers we have so far, which are
likely to change over time.

Ebola begins as fever, weakness, muscle pain, headache, and sore
throat, but soon progresses to vomiting, diarrhea, rash, and
impaired organ function. A large proportion of those infected
also bleed profusely, both internally and externally. It's
considered highly contagious, though it isn't transmitted through
the air — instead it's spread by bodily fluids like blood and
saliva, which can be very hard to avoid when someone is bleeding
heavily from every orifice.

Ebola first emerged in humans in 1976, and there have been more
than 18 outbreaks since then. There is currently no
vaccine and no cure.